In surgical procedures, the surgeon generally requires instruments capable of actuating in precise locations and directions. The surgical stapling apparatus and the clip applier are two examples of such instruments. Endoscopic surgical use of those instruments, in particular, poses special problems.
In laparoscopic surgery, after a patient's abdominal cavity is filled with gas, a trocar is utilized to puncture the skin of the patient's body cavity. When the obuator of the trocar is removed, a cylindrical tube or cannula from the trocar is positioned within the skin. This tube or cannula provides an opening through which the surgeon can access the inner body of the patient. The surgeon performs the surgical procedure by the insertion of instruments through the tube which is inserted into the body cavity of the patient.
These instruments generally possess long arms or shafts which pass through the tube. An actuation mechanism is located at the distal end of the arm or shaft which is inserted through the tube. A handle with the operating controls is located at the other end or proximal end of the arm, which is exposed externally during surgery. Thus, the surgeon can externally control the functions of the instrument.
However, because the walls of the tube rigidly constrain the angle at which the arm of the surgical instrument can be inserted and because the tube has restricted orientation with respect to the body cavity, the surgeon is afforded little adjustability in the location and angle of the actuation mechanism of the inserted surgical instrument. For the most part, the instrument is held in a parallel position relative to the trocar tube. Thus, a surgeon operating within the body cavity of a patient is restricted in the orientation of the surgical instruments used within the body cavity. In other words, the surgical instrument can be inserted into the patient's body at a limited angular range.
This limitation in adjustability conflicts with the requirements of the surgical procedure. For example, some of the body tissue to be operated on may lie in places difficult to reach or at angles which are difficult to accommodate. Furthermore, in any single procedure, the body tissue to be operated on will lie in various positions and angles.
Accordingly, the surgeon needs to be able to adjust the location and angle of the surgical instrument in order to accurately manipulate or fasten body tissue. Without any ability to adjust the orientation of the actuation mechanism, an entirely new trocar tube would have to be inserted into the patient's body at another location. Clearly, the insertion of additional trocar tubes is to be avoided.
For these reasons, it is desirable for a surgical instrument to have flexible movement in the area of the clip-applying, stapling or other actuation mechanism. However, designing an inexpensive and reliable articulation and rotational feature has many considerations.
By necessity, the actuation mechanism must be located at the distal part of the endoscopic arm while the controls must be located at the end of the instrument externally exposed during surgery so that the surgeon can access them. The drive rod and cable assembly which transmits the linear force runs the length of the instrument from the controls end to the actuation mechanism. To provide optimal flexibility, the articulation feature must operate at the end of the instrument within the body cavity near the actuation mechanism. Consequently, the linear force must be transmitted through the bent drive cable without creating a moment force. A moment would cause unwanted cartridge articulation; it might also make it difficult for the surgeon to maintain steady positioning of the instrument.
Further, this drive cable must be capable of repeated bending and straightening. To ensure reliability, a material capable of withstanding this repeated cycle must be utilized. In addition, the compressive and tensile forces exerted on the drive cable should be minimized.
In addition, speed as well as accuracy is desirable during surgical procedures. Frequently, quick adjustment of the orientation of the surgical instrument is critical. Furthermore, articulation should not require the exertion of additional pressure by the surgeon to trigger the instrument. The trigger pressure should remain as low as possible without risking accidental triggering.
Articulation of the arm of the surgical instrument provides significant adjustability to the actuation direction. This adjustability is immensely enhanced when used in conjunction with a rotation feature. Consequently, the articulation feature must accommodate a rotational feature. Furthermore, increased stability in the position of rotation adjustment is generally desirable. While a certain lack of stability in the rotational positioning of the arm of the surgical instrument could be tolerated if the instrument has no articulation feature, the presence of an articulation feature increases the need for stability in rotational positioning.
The surgeon only has two hands and one of his hands is needed to pull the trigger to actuate the mechanism. Consequently, the surgeon must rely upon the arm remaining at one rotation position so that the articulation feature can be adjusted accordingly. This situation is true in the reverse and is especially true if a number of iterations in adjustment is necessary. Thus, a means of stability for the rotational positioning feature and the articulation feature are essential aspects of a surgical instrument.